Technological Prerequisites

Technological Prerequisites : Technological Prerequisites George Macri ROMTELECOM S.A. Romania 5th Network Technologies Workshop .


Technological Prerequisites : Technological Prerequisites Internetworks Internet Protocols Internet Addresses Routing Subneting CIDR


What internetworks are : What internetworks are Start with lots of little networks Many different types ethernet, dedicated leased lines, dialup, ATM, Frame Relay, FDDI Each type has its own idea of addressing and protocols Want to connect them all together and provide a unified view of the whole lot


The unifying effect of the network layer : The unifying effect of the network layer Define a protocol that works in the same way with any underlying network Call it the network layer routers operate at the network layer There are defined ways of using: protocol over ethernet, ATM, FDDI protocol over serial lines (PPP) protocol over almost anything


Slide5 : The 7 Layer OSI Model


Slide6 : Protocol Stacks Layers: ethernet token ring atm dialup frame relay x.25 hdlc IP TCP / UDP Applications Network layer Transport layer


Layer Functions : Layer Functions Physical Data Link Network Transport IP TCP End to end reliability Forwarding best-effort Packet delivery Raw signal Application Mail, Web etc. Session Presentation


ISO seven layer model : ISO seven layer model 1: Physical layer moves bits using voltage, current, light, etc. 2: Data Link layer bundles bits into frames and moves frames between hosts on the same link


ISO seven layer model : ISO seven layer model 3: Network layer (e.g. IP) Makes routing decisions uses destination address in packet Forwards packet hop by hop encapsulates network layer packet inside data link layer frame different framing on different underlying network types Unreliable Single address space for the entire internetwork


ISO seven layer model : ISO seven layer model 4: Transport layer (e.g. TCP) end to end transport of datagrams encapsulates datagrams in network layer packets adds reliability by detecting and retransmitting lost packets uses acknowledgements and sequence numbers to keep track


ISO seven layer model : ISO seven layer model 5: Session layer not used in the TCP/IP network model 6: Presentation layer not used in the TCP/IP network model 7: Application layer Uses the underlying layers to carry out work


Layer interaction : Layer interaction Presentation Session Transport Network Link Physical Link Network Physical Physical Link Link Network Transport Session Presentation Application Application Network


INTERNET PROTOCOLS : INTERNET PROTOCOLS Internet protocols can be used for communications between heterogeneous systems; can be used for communications between systems connected in a LAN; can be used for communications between systems connected in a WAN; can be used for communications between a set of interconnected networks; Documents called RFCs (Requests For Comments), which are reviewed and analyzed by the IETF community; improvements, additions and refinements of protocols are published in new RFCs (see ftp://ftp.rs.internic.net., ftp://ftp.ripe.net/). Looking at all RFCs, you can see the history of the development of Internet protocols, people and companies that have contributed to this TCP and IP are the best known of the Internet protocols and very often the term TCP/IP refers to the whole family of protocols.


TCP/IP Model : TCP/IP Model Message Segment Datagram Frame Bit 5 4 3 2 1


TCP/IP is a 5 Layered model : TCP/IP is a 5 Layered model Layers 1 and 2 are not actually defined by TCP/IP , as TCP/IP was defined to be independent of physical media .


Slide16 : Layer 3 is the Internet Protocol (IP) layer This provides a basic datagram service ICMP (Internet Control Message Protocol) is normally provided in this layer ICMP reports problems in transmission of datagrams ARP (Adress Resolution Protocol) RARP (Reverse Address Resolution Protocol)


Slide17 : In layer 4 are 2 possible protocols : TCP (Transport Control Protocol) and UDP (User Datagram Protocol) . TCP provides a reliable service with error correction and flow control . The cost of providing a reliable service is more overhead in connection setup and closedown, processing power for correcting errors and data transmission, but some applications need reliability irrespective of cost. UDP just extends IP’s connectionless datagram service to applications that do not require reliability . UDP datagrams can be sent to a network without the overhead of creating and maintaining a connection


Slide18 : Layer 5 is the Application layer This layer provides services suitable for the different types of application that might wish to use the network . It does not provide the application itself . For example : SMTP , FTP , Telnet ...


TCP/IP : TCP/IP


Internet Protocols : Internet Protocols PPP HDLC SLIP LAPB Public telephone network LAN X.25 Ethernet/IEEE 802.3 ARP RFC 826 IP RFC 791 Telnet RFC 854 FTP RFC 959 SMTP RFC 821 SNMP TCP RFC 793 UDP RFC 768 DNS RFC 1035 NFS RPC RIP RFC 1058 ICMP RFC 792 Routing protocols BGP OSPF IGRP EIGRP


Slide21 : There is a protocol for mail that defines a set of commands and messages that one machine sends to the other, for example, a conversation between machines linkguide.ici.ro and mail.iob.ro: Linkguide: HELO linkguide.ici.ro Mail.iob.ro: 250 mail.iob.ro - HELO Linkguide.ici.ro Linkguide: MAIL From: Mail.iob.ro: 250 MAIL accepted Linkguide: RCPT To: Mail.iob.ro: 250 Recipient accepted Linkguide: DATA Mail.iob.ro: 354 Start mail input; end with , Linkguide: Date: Sat, 26 Jul 96 14:23:34 +02 Linkguide: From: gmacri@linkguide.ici.ro Linkguide: To: mihai@mail.iob.ro Linkguide: Subject: helo Linkguide: text of the message Linkguide: . Mail.iob.ro: 250 OK Linkguide: QUIT Mail.iob.ro: 221 mail.iob.ro Service closing transmission channel The protocol assumes that we have a reliable way of command and message communication SMTP mail exchange as an example


TCP/IP Architecture Terms : TCP/IP Architecture Terms Host B Ethernet Driver router IP eth drv t.r. drv


Encapsulation : Encapsulation Lower layers add headers (and sometimes trailers) to data from higher layers Data Data Data Data Header Header Header Header Header Header Application Transport Internet Network Access


IP Addresses : IP Addresses Purpose Basic Structure Network mask Special addresses


Purpose of an IP address : Purpose of an IP address Unique Identification of Source Sometimes used for security or policy-based filtering of data Destination So the networks know where to send the data Network Independent Format IP over anything


Basic Structure of an IP Address : Basic Structure of an IP Address 32 bit / 4 byte number: (e.g. 204.152.8.1) Decimal Representation: Binary Representation: 152 8 1 204 11001100 10011000 00001000 00000001


Address Structure Revisited : Address Structure Revisited Hierarchical Division in IP Address: Network Part (Prefix) describes which physical network Host Part (Host Address) describes which host on that network Boundary can be anywhere not necessarily at a multiple of 8 bits Network Host 205 . 154 . 8 1 11001101 10011010 00001000 00000001


Network Masks : Network Masks Define which bits are used to describe the Network Part Different Representations: decimal dot notation: 255.255.248.0 number of network bits: /19 Binary AND of 32 bit IP address with 32 bit netmask yields network part of address


Slide29 : Subnetting One class address (either B or C) space could be too large for a given organization, or for a certain site of the organization. Subnetting divides a single network address into many subnet addresses, so that each subnetwork can have its own unique address. A subnet is defined by applying a bit mask (the subnet mask) to the IP address. If a bit is 1 in the mask, the equivalent bit in the address is interpreted as a network bit. If a bit in the mask is 0, the bit belongs to the host part of the address. Ex: mask to divide the 193.226.2.0 address into 4 subnets: 11111111 11111111 11111111 11000000


Example Prefixes : Example Prefixes 137.158.128.0/17 (netmask 255.255.128.0) 198.134.0.0/16 (netmask 255.255.0.0) 205.37.193.128/26 (netmask 255.255.255.192) 10001001 10011110 1 0000000 00000000 11000110 10000110 00000000 00000000 11001101 00100101 11000111 10 000000 11111111 11111111 1 0000000 00000000 11111111 11111111 11111111 11 000000 11111111 11111111 00000000 00000000


Old-Style Classes of Address : Old-Style Classes of Address Different classes used to represent different sizes of network (small, medium, large) Class A networks: x.0.0.0 - 16.777.215 host addresses 8 bits network, 24 bits host (/8, 255.0.0.0) First byte in range x=1-127 Class B networks: x.y.0.0 - 65.536 host addresses 16 bits network, 16 bits host (/16 ,255.255.0.0) First byte in range x=128-191 y=0-254 Class C networks: x.y.z.0 - 256 host address 24 bits network, 8 bits host (/24, 255.255.255.0) First byte in range x=192-223 y,z=0-254


Slide32 : IP Address Structure - Class-full Network address Host address Address format 32 bits Class A network=8 bits Class B network=16 bits Class C network=24 bits Class D (multicast) Class E (reserved) 0 1 0 1 1 0 1 1 1 0 1 1 1 1


Special Addresses : Special Addresses All 0’s in host part: Represents Network e.g. 193.0.0.0/24 e.g. 138.37.128.0/17 All 1’s in host part: Broadcast e.g. 137.156.255.255 (137.156.0.0/16) e.g. 134.132.100.255 (134.132.100.0/24) e.g. 190.0.127.255 (190.0.0.0/17) 127.0.0.0/8: Loopback address (127.0.0.1) 0.0.0.0: Various special purposes


Slide34 : TCP/IP Basics: Physical & Datalink


The Physical and Datalink layer : The Physical and Datalink layer Ethernet IEEE and ISO Token Ring FDDI SLIP PPP ISDN


Ehernet : Ehernet Network access protocol The medium for communication between two machines directly connected can be: coax, twisted cable, telephone link, radio link, satellite link, etc. The lowest layer of protocols provides functions that manage the data transmission specific to a certain physical medium. Classes of links Point to point Broadcast Non-broadcast multi-access Ethernet/IEEE 802.3 is a coaxial based bus cabling system developed by Digital Equipment Corporation, Intel, Xerox (DIX) Ethernet was the technological basis for the IEEE 802.3 specification Both of them specify the CSMA/CD (Carrier Sense Multiple Access with Collision Detection), also referred as “listen while talk” (LWT) Both are broadcast networks


Ethernet Topologies : Ethernet Topologies Fiber concentrator Transceivers 10/100/1000 Base F


The Ethernet frame : The Ethernet frame This Ethernet frame encapsulates the TCP/IP protocol and is responsible for transporting it across the cabling system to layer 2 of the destination device , whether it’s a Router , Gateway or end node .


MAC addressing : MAC addressing The ethernet frame uses addresses referred to as MAC (Medium Access Control) MAC addresses identify the specific network cards These are 48 bits long Each network card has a unique address configured by its manufacturer


Slide40 : The LAN card will accept only 3 types of MAC address . Unicast - Frames with destination to the exact MAC address . Broadcast - Has all 48 bits set to binary 1 (or Hex FF FF FF FF FF FF) . This type of frame is used when the sender does not know the destination MAC address it tries to communicate , so we broadcast to all . Multicast - Addressing to groups of LAN cards that are related in some way . The LAN cards have to be configured to know they are part of a multicast group .


The type field : The type field The Type field identifies different protocols . A computer running multiple protocols can easily differentiate between them , and path the contents to the relevant layer . TCP/IP Generally uses 3 Ethernet types registered in IEEE .


CRC - Cyclic Redundancy Check : CRC - Cyclic Redundancy Check At the end of the frame is a CRC . This is a 32 bit value that is calculated from all the bits of the Ethernet frame and its contents , but ignoring the preamble and the CRC itself . The remote node does the same calculation and compares the CRC . If the value is different , the LAN card will not pass the Frame to the network layer .


The service provided by Ethernet : The service provided by Ethernet The medium access mechanism used by Ethernet is CSMA/CD (Carrier Sense Multiple Access with Collision Detection) . This allows nodes on the network to manage shared access to the cable , but it restricts the length of the cabling , and the number of nodes that use it . They are not specific to Protocol , therefore for TCP/IP .


Ethernet Packet size : Ethernet Packet size Minimum packet size - 64 octets Maximum packet size - 1518 octets The sizes above include all the frame apart from the preamble . Because of the frame header fields , the CRC and the overhead of the IP and TCP or UDP higher layer protocols , the amount left for useful application data is less then 1518 .


Slide45 : To give an example : The Ethernet frame overhead consists of 18 octets and the higher layer protocols often need 40 octets . That leaves 1460 (1518-40-18=1460) octets for application data .


IEEE and ISO systems : IEEE and ISO systems IEEE 802.3 uses CSMA/CD . IEEE 802.4 uses a token mechanism on a bus . IEEE 802.5 and FDDI (IS9314) use a token passing mechanism on a ring .


LLC (Logical Link Layer) : LLC (Logical Link Layer) For LAN’s , layer 2 is split to 2 sublayers . The lower is MAC and above we have the LLC , which has the standard number IEEE 802.2 . One of the major functions of LLC is to differentiate between the different types of network layer protocols , in a similar way to the type field of Ethernet .


Ethernet : Ethernet


Token Ring : Token Ring


FDDI : FDDI


Encapsulation : Encapsulation The type field specifies the upper-layer protocol to receive the data after Ethernet processing is complete The CRC (Cyclic Redundancy check) is created by the sender and recalculated by the receiver The frame length (header, data, and CRC) 64-1518 bytes Application TCP IP Ethernet E I T Data C I T Data T Data Data E I T Data C I T Data T Data Ethernet Ethernet IP TCP Application


The IEEE 802.3 frame : The IEEE 802.3 frame The IEEE 802.3 frame has the same general format as DIX Ethernet (Ethernet_II) frame . The Type field in Ethernet DIX is the Length field in IEEE 802.3 THE FCS (Frame Check Sequence) is instead of CRC As there is no Type field , it is not possible to detect which network layer protocol is carried in the MAC layer The MAC frame consists of only addresses , length and FCS. It is the function of LLC to separate the different network layer protocols .


IEEE 802.3 frame : IEEE 802.3 frame 46-1500 Octets


Bridging TCP/IP : Bridging TCP/IP Bridging between IEEE LAN’s is often promoted as transparent to any protocol above the MAC layer . This will bring expectations that there are no particular problems with TCP/IP . There are 4 issues that need consideration : The length field for the 802.3 bus. Encapsulation on bus networks. The maximum frame sizes. The representation of MAC addresses.


Length fields : Length fields The IEEE 802.3 CSMA/CD network has a length field immediately before the LLC . Other IEEE networks do not . Bridging will at least involve changing the content of the frame and recalculating the FCS . This action will be totally transparent to the network planners .


Frame size : Frame size For TCP/IP , the transmitted frame size is determined by the Maximum Transfer Unit (MTU) set in the driver software for the LAN interface . It is possible on most TCP/IP implementations to modify the MTU to match the number of data octets carried by the Link Layer protocol . Setting the MTU’s of each interface on a Token Ring to 1492 will prevent its frames from being to large for bridging to IEEE 802.3 . This reduction will limit Token Ring efficiency .


Representation of MAC addresses : Representation of MAC addresses The IEEE 802.1 committee defined how LAN’s should represent 48 bit MAC addresses as a bit stream on the cable . IEEE 802.3 and 802.5 committee chose to represent these addresses higher in the protocol . IEEE 802.3 and 802.5 represent differently the MAC address . Bridges now have to be wise and not only reverse the address but also to calculate the FCS .


Example of vendor-dependant Ethernet addresses : Example of vendor-dependant Ethernet addresses Prefix Manufacturer 00:00:0C Cisco 00:00:95 Proteon 00:00:A2 Wellfleet 00:00:C0 Western Digital 00:AA:00 Intel 02:60:8C 3Comm 08:00:09 Hewlett-Packard 08:00:10 AT&T 08:00:0B Unisys 08:00:20 Sun 08:00:2B DEC 08:00:46 Sony 08:00:5A IBM AA:00:03 DEC AA:00:04 DEC


TCP/IP Basics: Serial Connections : TCP/IP Basics: Serial Connections


SLIP - Serial Line Internet Protocol : SLIP - Serial Line Internet Protocol In some situations , it is advantageous to use asynchronous Serial lines to carry TCP/IP protocols , either by : Dialup modems Modems on private wires through an asynchronous network Direct connection between 2 computers


SLIP functionality : SLIP functionality LAN Host Asynchronous connections V.24/RS232C Dialup modem link Modem link Direct connection PC’s with SLIP


SLIP frame format : SLIP frame format SLIP defines 2 special characters : SLIP END - 0xC0 SLIP ESC - 0xDB Datagrams sent using SLIP are framed SLIP END characters .


SLIP frame format : SLIP frame format


PPP - Point to Point Protocol : PPP - Point to Point Protocol PPP came to overcome a number of limitations of SLIP . PPP has been designed to operate over both : asynchronous (start/stop) connections , and bit oriented synchronous systems .


Slide65 : PPP provides more then just a simple connection between hosts . It also defines several management and testing functions to deal with line quality , option negotiation and the setup of IP addresses .


The service provided by PPP : The service provided by PPP PPP provides a Point to Point connection between 2 TCP/IP systems for the transfer of IP datagrams . PPP can operate over virtually any serial link interface . The only limitation is that it requires a full duplex connection .


Slide67 : It does not need serial interface control signals , but the standard recommends it for performance improvements . There is no restriction for the speed used for PPP .


The PPP frame : The PPP frame The address field is all 1’s. The control octet contains the value 0x03. The protocol field defines the protocol carried by this frame : Link Control Protocol - 0xC021 Network Control Protocol - 0x8021 Internet Protocol - 0x0021


Slide69 : PPP can multiplex data from many sources, which makes it practical for high speed connections between bridges or routers.


TCP/IP Basics: Network Layer : TCP/IP Basics: Network Layer


Why do we need IP protocol layer? : Why do we need IP protocol layer? Although the services provided by TCP protocol are needed by many applications, there are still some kind of applications that don’t need them; However, there are some services that every application needs. The services that every application needs are put together into the IP protocol layer; IP protocol provides the basic service for the transmission of a datagram from one machine to another machine which do not need to be connected directly; As a result, TCP calls on the services of IP; Like TCP, IP protocol layer can be viewed as a library of routines that TCP calls on, but which is also available to applications that don’t use TCP


IP - Internet Protocol : IP - Internet Protocol IP is described as a “connectionless datagram service” . Datagrams are packets of information that can be destined for one , many or all stations (unique , multicast or broadcast) - provide addressing. There is no requirement for the intended recipient/s to acknowledge whether the datagram was received (no flow control, no end-to-end data reliability). As IP is connectionless , no specific route is defined between 2 communicating nodes , so datagrams traveling can travel through different routes and reach destination in a different order (no sequencing and allow for fragmentation). One of the major roles of IP layer is to make it unnecessary for higher layer protocols to understand anything about the physical capabilities of the media supporting them . Note : This is important for application developers writing programs on top of the transport layer with no variations because of the different kind of media used .


The IP Architecture : The IP Architecture Message Segment Datagram Frame Bit 5 4 3 2 1 ( ) ( ) ( ) ( ) 1 0800 8035 0806


Encapsulation : Encapsulation Both the header and data of the IP datagram become the datalink frame of whichever network they happen to be on.This is called encapsulation . Protocol number identifies the protocol in the layer above IP to which the data is passed (/etc/protocols) 0 IP pseudo protocol number 1 ICMP 6 TCP 17 UDP


Fragmentation and Reassemble : Fragmentation and Reassemble IEEE 802.3 and Ethernet systems have maximum data sizes of 1492 and 1500 octets respectively . IEEE 802.5 frames is not defined , but in practice it is usually no greater then 8192 octets . This size limit seen by IP is known as the Maximum Transfer Unit (MTU) . The MTU can be adjusted for each interface , but it’s not necessary unless bridging different LAN technologies .


IP datagram Format : IP datagram Format


Slide77 : Version - 4 bits Version of the IP protocol Current version is 4 Internet Header Length - 4 bits For easy finding of beginning of data . Normally the value is 5 indicated no options are used . Type Of Service - 8 bits The first of 3 bits are used to indicate 1 of 8 levels of priority . Some Routers Ignore these flags . Total length - 16 bits The total length of the IP datagram The size of data is computed from the total length field and IHL . Identification - 16 bits This is an integer value used to help identify all fragments of a datagram . This field is unique for each new datagram .


Slide78 : Flags - 3 bits The 2 low order bits are used as flags to control fragmentation . The low order bit , if 0 , indicates the last fragment of a datagram - MF (More Flag) . The middle bit is used to indicate that the datagram should not be fragmented - DF (Do not Fragment) . Fragment Offset - 13 bits Used in a fragmented datagram to indicate the position that the fragment occupies . Time To Live (TTL) - 8 bits This prevents datagrams to get routed in a loop . If it’s set to 0 , a router should discard the datagram . The recommended value is 32 , but it can be set to a maximum of 255 too . Protocol - 8 bits The transport layer protocol carried by this datagram . It tells the IP layer where to path the datagram . 17 - UDP 6 - TCP 1 - ICMP


Slide79 : Header checksum - 16 bits It protects only the header and not the data . The reason is because the checksum must be recalculated every time it passes through a router . Other parameters change too . Source IP address - 32 bits Destination IP address - 32 bits Data variable This includes the headers of higher layer protocols and user’s data .


Routing IP Datagrams : Routing IP Datagrams Target


IP Routing : IP Routing SubNet Direct Connection local host same subnet default gateway local host default gateway local host same subnet next-hop Subnet Default Gateway


IP algorithm : IP algorithm 1. Search the routing table for an entry that matches the complete destination IP address (network ID or host ID). If found, send the packet to the indicated next-hop router or to the directly connected interface. (second interface or ppp) 2. Search the routing table for an entry that matches just the destination network ID. If found, send the packet to the indicated next-hop router or to the directly connected interface. (local networks) 3. Search the routing table for an entry labeled “default”. If found, send the packet to the indicated next-hop router


ARP - Address Resolution Protocol : ARP - Address Resolution Protocol If we wish to connect to a remote computer we must know it’s IP address , but we do not need to know it’s MAC address . ARP was invented for this reason . It relates IP’s to MAC addresses only on media that supports broadcasts . Each node maintains a cache called the ARP cache , which holds a table of IP’s against MAC addresses .


How ARP works : How ARP works When IP is requested to send a datagram to another IP address , it first looks in the ARP cache to find the corresponding MAC address . If there is no entry it then attempts to look for it using ARP . In order to do this ARP sends an ARP request datagram to all LAN cards using a broadcast address .


Slide85 : ARP uses its own Ethernet type 0x0806 for these requests , so they are passed to the ARP software in all nodes within the broadcast area . All cards on a network read this request datagram and any that discover a match between their IP and the requested IP reply with an ARP response . If a response is received , the answer is entered to the ARP cache for future use . If none is received , the request is repeated . ARP datagrams are not passed through routers , as a router operates at the IP layer and will not relay MAC broadcast traffic . This makes routers a good buffer between broadcast domains and prevent flooding networks .


ARP commands : ARP commands arp command can be used to display the content of the ARP table; Formats: arp -a ! displays all the entries in the ARP table; arp ! displays the entry for specified arp -d ! deletes an entry for arp -s ! adds a new entry


RARP - Reverse ARP : RARP - Reverse ARP RARP is intended for use with devices that cannot store their IP address , usually diskless workstations. RARP , like ARP , operates directly over the datalink layer and has an Ethernet type 0x8035 . Nodes acting as RARP servers that find a match for the MAC address in their RARP tables will reply with the corresponding IP address in a RARP response .


Slide88 : This system requires that at least one server is present and that the server has a table defining which IP addresses should be used by each MAC address .


ICMP - Internet Control Message Protocol : ICMP - Internet Control Message Protocol Even though IP is a datagram service and there is no delivery guarantee , ICMP is provided within IP and can generate error messages regarding datagram delivery . ICMP uses IP datagrams to carry its messages back and forth between relevant nodes .


Slide90 : ICMP error messages are generated by a node recognizing there is a transmission problem and they are sent back to the originating address of the datagram that caused the problem .


General format of ICMP message : General format of ICMP message Type (8): specifies the type of ICMP message Code (8): used to specify parameters of the message that can be encoded in a few bits Checksum (16): checksum of the entire ICMP message Parameters (32): used to specify more lengthy parameters Information (variable):provides additional information related to the message ECHO and ECHO REPLY - mechanism for testing if communication is possible between two entities. A host can send the ICMP ECHO message to see if a remote IP is up and operational. When a system receives an echo message, it send the same packet back to the source host in an ICMP ECHO REPLY message. The ping command uses this message. A TIME EXCEEDED message is sent by a gateway if the ttl value of a datagram expires (becomes zero). This facility is used by the traceroute command. Type (8 bits) Code (8 bits) Checksum (16 bits) Parameters (32 bits) Information (variable)


Slide93 : Type field 0 3 4 5 8 11 12 13 14 15 16 17 18 Echo reply Destination unreachable Source quench Redirect Echo request Time exceeded for datagram Parameter problem on datagram Time stamp request Time stamp reply Information request Information reply Address mask request Address mask response Message Type


The ping command : The ping command ping it is a simple function, extremely useful for testing the network connection; it allows the network administrator to determine whether further testing should be directed toward the network (the lower layers) or the application (the upper layers) if ping shows that packets can travel to the destination system and back, the problem is probably in the upper layers If packets can’t make the round-trip, lower protocol layers are probably at fault Basic format ping [] [] The host name or IP address of the remote host being testyed. Defines the size in bytes of the test packets. This field is only required if the count field is going to be used. Default packet size is 56 bytes. The number of packets to be sent in the test. Default number is usually 5.


ping example : ping example Examples #ping ftp.ripe.net info.ripe.net is alive # ping -s ftp.ripe.net 100 10 PING info.ripe.net: 100 data bytes 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=0. time=1070. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=1. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=2. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=3. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=4. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=5. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=6. time=990. ms 108 bytes from info.ripe.net (39.13.5.97): icmp_seq=7. time=980. ms ----info.ripe.net PING Statistics---- 8 packets transmitted, 8 packets received, 0% packet loss round-trip (ms) min/avg/max = 980/998/1070


traceroute - Tracing routes : traceroute - Tracing routes is the program that can help the network administrator locate the problem when something is down between the local host and a remote destination traces the route of UDP packets from the local host to a remote host prints the name (if it can be determined) and IP address of each gateway along the route to the remote host uses two techniques: small ttl values and invalid port number


traceroute - Tracing routes : traceroute - Tracing routes Operation traceroute sends out 3 UDP packets with ttl value set to one the first gateway decrement ttl and gets the value zero. The first gateway will send back to the source host an ICMP TIME EXCEEDED message as error message traceroute displays one line of output for each gateway from which it receives an ICMP TIME EXCEEDED message traceroute will then increment by one the ttl value and sends again 3 UDP packets the flow of packets tracing to a host three hops away is illustrated below When the destination host receives a packet from traceroute, it returns back an ICMP “Unreachable Port” message. This happens because traceroute intentionally uses an invalid port number (33434) to force this error. When traceroute receives the “Unreachable Port” message, it knows that it has reached the destination host, and it terminates the trace. In this way, traceroute is able to develop a list of the gateways, starting at one hop away and increasing one hop at a time, until the remote host is reached.


traceroute example : traceroute example # traceroute ftp.ripe.net traceroute to info.ripe.net (39.13.5.97), 30 hops max, 40 byte packets 1 agsici1.ici.ro (192.162.16.25) 20 ms 10 ms 0 ms 2 Vienna-EBS1.Ebone.NET (192.121.159.97) 870 ms 870 ms 870 ms 3 Paris-EBS2.Ebone.net (192.121.156.17) 900 ms 890 ms 890 ms 4 Stockholm-ebs.ebone.net (192.121.154.21) 920 ms 930 ms 960 ms 5 Amsterdam-ebs.Ebone.NET (192.121.155.13) 970 ms 990 ms 970 ms 6 Amsterdam.ripe.net (193.0.15.130) 1000 ms 970 ms 970 ms 7 info.ripe.net (39.13.5.97) 1040 ms 970 ms 990 ms


Flow of traceroute packets : Flow of traceroute packets ping program First router Second router Third router decrements ttl to 0 return error “TIME EXCEEDED” ttl=1 ttl=2 ttl=3 decrements ttl to 1 forward decrements ttl to 0 return error “TIME EXCEEDED” decrements ttl to 2 forward decrements ttl to 1 forward received at destination port unreachable Return error “port unreachable”


Slide100 : ICMP has it’s own IP protocol number (1) so the IP layer knows when it receives them. Even though ICMP uses the IP layer, it is considered as being within IP, because it does not necessarily provide any service to the layers above.


ICMP types 0 and 8 - echo : ICMP types 0 and 8 - echo The most common ICMP messages used for diagnostics are type 0 and 8. These are generated by Ping. Ping sends ICMP type 8 datagrams to a node and expects an ICMP type 0 reply, returning the data sent in the request.


ICMP echo datagram (0 or 8) : ICMP echo datagram (0 or 8)


Note : : Note : How can Ping generate ICMP echo requests if ICMP does not provide a service to Ping ? A Ping implementation does not use ICMP to generate the request. It merely mimics what ICMP would do as a program that operates over the IP layer. Ping generates an IP datagram with a data field that equates to ICMP echo request (protocol number 1 and the first octet of data is 8 - ICMP echo request). It then adds the rest of the fields including the data pattern that it expects to be echoed.


ICMP type 3 - destination unreachable : ICMP type 3 - destination unreachable If a router is unable to deliver a datagram, it can return the destination unreachable ICMP datagram to indicate why. The code field is used to identify the cause of failure. The values in the code field help to pinpoint the reason for the datagram failure to arrive its destination.


ICMP type 3 - Destination Unreachable : ICMP type 3 - Destination Unreachable


Code value : Code value 0 Network unreachable 1 Host unreachable 2 Protocol unreachable 3 Port unreachable 4 Fragmentation needed and the do not fragment bit set 5 Source route failed Meaning


Slide107 : If a router is unable to deliver a datagram , it can return the destination unreachable ICMP datagram to indicate why . Network unreachable - The network specified in the IP address cannot be found . The IP address and routing tables should be checked . This error message is only generated by a router . We can find where the error occurred , from the source address in IP header that carried the ICMP message . Host unreachable - The datagram reached the router which is directly connected to the destination network, but failed to communicate with the host. This message is generated by a router only .


Slide108 : Protocol unreachable - The datagram reached the destination host , but the particular protocol carried in the datagram is not available . Port unreachable - A host sends the message that the particular application layer service is not available . Fragmentation needed and the do not fragment bit set - Normally comes from a router , indicating that it needs to fragment the datagram , but is instructed not to by the do not fragment (DF) bit in the flags field of the IP header . This fault is uncommon , DF is normally used on diskless workstations booting via TFTP . TFTP has only 512 octets of user data . Check MTU size .


Slide109 : Source route failed - If we specified a route and the datagram failed to complete the route , we will get this error . The point of failure will be the router that generated the ICMP message .


ICMP type 4 , code 0 - Source Quench : ICMP type 4 , code 0 - Source Quench The format of the datagram is the same as destination unreachable , but with a type of 4 and a code of 0 . Source quench gives a router or a host the ability to request that a source of datagrams will slow down . Source quench will occur if a node is running low on buffer resources and is unable to process datagrams quickly enough .


ICMP type 5 - route change request : ICMP type 5 - route change request It is used only by routers . A router that knows that it is not the optimum router for a particular destination , uses the relevant field of a route change request to suggest a more suitable router .


ICMP type 11 - time exceeded for datagram : ICMP type 11 - time exceeded for datagram The format is the same as destination unreachable . It can be sent in 2 situations : From a router - Indicating that the TTL in the IP header has been decremented to 0 . It indicates that the original Time To Live was not suitable to the number of hops needed . From a node - An attempt to recreate the original datagram by reassembly of fragments failed . The code value is 1 .


ICMP type 12 - Parameter problem message : ICMP type 12 - Parameter problem message Indicates that a wrong argument has been used with an option field in the IP header . It can also indicate an error in the implementation of IP . It’s sent only if the datagram has been discarded . The pointer field indicates the position of the octet position of the suspect field .


ICMP types 13,14 - Time stamp request & reply : ICMP types 13,14 - Time stamp request & reply This message is used to obtain the time from a clock in a distant machine . It is rarely used today .


ICMP types 15,16 - information request : ICMP types 15,16 - information request This message is used to obtain the network number of the requesting host if it’s unknown . It can be used in dial in systems using SLIP, as a method for allocating the appropriate network addresses for each end of the link .


ICMP types 17,18 - Address mask request : ICMP types 17,18 - Address mask request Used to allow a node to discover the subnet mask of the network it is connected to . The node can send the request to a known address or to broadcast .


Transport Protocol Ports : Transport Protocol Ports Port 0 - Special use Ports 1 - 255 - Well-known ports Ports 256 - 1023 - Reserved ports Ports 1024 - 4999 - Dynamic client ports Ports 5000 - 65,535 - Fixed server ports The address of an application within a host


User Datagram Protocol : User Datagram Protocol Connectionless delivery service Uses the IP layer service Does not add reliability to the IP protocol Enables distinguishing among multiple destinations within a host computer End point


UDP Protocol Header Format : UDP Protocol Header Format Fragmentation What if the packet size is larger then 1500? It is divided to 1500xN frames. fragmentation flags are set


Slide121 : Flow using Datagrams (UDP) Server socket() bind() Client socket() sendto()/recvfrom() closesocket() sendto()/recvfrom() closesocket()


Transmission Control Protocol : Transmission Control Protocol Connection based communication Uses the IP layer service Provides reliable service Enables distinguishing among multiple destinations within a host computer


TCP - Transmission Control Protocol : TCP - Transmission Control Protocol TCP is the protocol layer responsible for making sure that the commands and messages are transmitted reliably from one application program running on a machine to another one on the other machine A message is transmitted and then a positive acknowledgement is being waited for If the positive acknowledgement does not arrive in a certain period of time, the message is retransmitted Messages are numbered in sequence so that no one is being lost or duplicated; Messages are delivered at the destination in the same order they were sent by the source If the text of a mail is too large, the TCP protocol will split it into several fragments called “datagrams” and it makes sure that all the datagrams arrive correctly at the other end where they are reassembled into the original message The TCP protocol layer provides all the functions that are needed for many applications and it is better to put them together on a separate protocol rather than being part of each application TCP can be viewed as forming a library of routines that many applications can use when they need reliable network communication with an application on another computer TCP provides also flow control and congestion control


TCP Protocol Format : TCP Protocol Format Source Port Destination Port Sequence Number Acknowledgment Number Checksum (16) Urgent Pointer Options(If any) Padding Data (variable length) 0 4 10 16 24 31 Offset Reserv Flags(6) Window (16 bits)


Establishing and closing TCP Connections : Establishing and closing TCP Connections Three-way handshake Close time SYN ACK SYN+ACK Open FIN ACK ACK FIN


Sliding Windows : Sliding Windows Positive acknowledgment with retransmission Sliding window transmission time segment 1 segment 2 ack1 ack2


Application Addresses: Sockets : Application Addresses: Sockets On a network server, normally several application programs are running at the same time: FTP server, telnet server, mail server, www server, gopher server, etc.; TCP must know to which program to deliver the received message; If you want to connect to the FTP server it is not enough to know the IP address of the server, you have to specify that you want to talk to the FTP server program; This is done by having “the well-known sockets” - TCP ports - (see the file /etc/services on a UNIX machine): In a file server session, e.g., two different applications are involved: FTP server and FTP client The client program gets commands from the user and passes them to the FTP server program; There is no need for the client FTP program to use a well know socket number, because nobody is trying to find it, as opposed to the FTP server program which have to have a well-known socket number, so that people can open connections to it and start sending commands; The client FTP program asks the network software to assign it a port number that is guarantee to be unique, for example 1236 if that number was free; A connection is identified by four numbers: connection 1: 192.162.16.2, 1236 193.230.3.120, 21 connection 2: 192.162.16.2, 1237 193.230.3.120, 21 Two connections are different if at least one number is different


Application Addresses: Sockets : Application Addresses: Sockets Socket = IP address + port # Message Segment Datagram Frame


Slide129 : Well-known TCP ports 21 - FTP server 23 - telnet server 25 - SMTP mail server 53 - domain nameserver 109 - POP2 server 110 - POP3 server


Flow using Streams (TCP) : Flow using Streams (TCP) Server socket() bind() listen() accept() send()/recv() closesocket() Client connect() send()/recv() closesocket() socket()


ROUTING : ROUTING The source and the destination hosts are on the same LAN There is no decisions for routing; The packet is transmitted on the cable (coax, twisted cable, optical fiber); Every computer connected to the LAN will receive it. That computer which finds that the destination Ethernet address in the header is equal to his Ethernet address will get the message, the others will discard it. Note that the address of each computer on the LAN begins with the same network number Routing table for host A:


Example of complex configuration : Example of complex configuration A .1 D .4 .1 .2 .1 G .4 .2 .1 H I J .2 K .3 L .4 .5 .1 M .2 N 192.162.16. 193.230.3. 193.230.4. 193.230.5. 193.230.6. backbone network with Internet connectivity eth0 ec0 ec0 eth0 eth0 sl0 sl0 sl0 Routing tables net gw int. M: 193.230.5 none eth0 193.230.6.2 sl0 193.230.4 193.230.5.1 eth0 193.230.3 193.230.5.1 eth0 192.162.16 193.230.5.1 eth0 default 193.230.6.2 sl0 I 193.230.5 none eth0 193.230.4.1 sl0 193.230.3 193.230.4.1 sl0 192.162.16 193.230.4.1 sl0 default 193.230.5.5 eth0 H 193.230.3 none ec0 193,230.4.2 sl0 192.162.16 193.230.1 ec0 default 193.230.4.2 sl0 A 192.162.16 none eth0 default 192.162.16.4 eth0 sl0 ec1


Routing table initialization and updating : Routing table initialization and updating Initialization of routing table Normally at startup time by executing script command files; Static routes route add route add 192.162.16.0 192.162.16.4 1 route add 193.230.3.0 192.162.16.4 1 route add default 192.162.16.4 1 netstat -rn displays the routing table on a UNIX machine Static routes have the disadvantage that they do not adapt to the changes in the network topology Dinamic routing protocols are run to update the routing table so that they reflect the changes in topology Router classes dedicated routers - special purpose equipment Cisco, Wellfleet, Proteon, Telebit cheap router sollution: - public domain software for PCs ka9q, PCROUTE, Linux, Free BSD, etc.


Routing protocols : Routing protocols Types of routing protocols Interior Gateway Protocol (IGP): RIP, IGRP, OSPF, Hello Exterior routing Protocol (EGP): BGP, EGP AS1 AS2 EGP IGP IGP


Autonomous System Number : Autonomous System Number An Autonomous System Number (AS) is a set of routers under a single technical administration, using an interior gateway protocol and an exterior gateway protocol to route packets to other ASs. An AS is a connected group of IP networks run by one or more network operators which has a single and defined routing policy. AS number is a 16 bit number (65535 unique AS numbers). It is a finite amount of address space. Sometimes, the term AS is misunderstood and used for grouping together a set of prefixes which belong under the same administrative umbrella. AS number are assigned by RIPE in Europe


Example for routing : Example for routing EBONE EUROPANET Access to Internet National Network BGP4 BGP4 IGRP static IGRP IGRP IGRP


CIDR - Classless Inter-Domain Routing : CIDR - Classless Inter-Domain Routing Internet Service Provider Internet 193.230.0.0 193.230.1.0 193.230.02.0 193.230.3.0 00000000 00000000 11100110 11000001 network host 11100110 11000001 00000001 00000000 00000000 00000010 11100110 11000001 11000001 1110010 00000011 00000000 Prefix Host Classless representation Class-full representation 193.230.0.0 193.230.1.0 193.230.2.0 193.230.3.0 customers


Example of CIDR configuration (supernetting) : Example of CIDR configuration (supernetting) Using BGP4 routing protocol, all the 4 C class addresses (193.230.0.0, 193.230.1.0, 193.230.2.0, 193.230.3.0) can be advertised like one entry in the routing table: router bgp 3233 agregate-address 193.230.0.0 255.255.252.0 summary-only neighbor 192,121,159,97 remote-as 1755 neighbor 193.226.27.86 remote-as 2614 Using BGP4 routing protocols, all the 256 C addresses of the block 193.230.0.0 - 193.230.255.255 can be advertised like one entry in the routing table: router bgp 3233 agregate-address 193.230.0.0 255.255.0.0 summary-only neighbor 192,121,159,97 remote-as 1755 neighbor 193.226.27.86 remote-as 2614


Slide139 : IPng Features/Functionality Expanded Address Space Autoconfiguration Real-time/Multimedia support Integrated Security support IPv4 IPv6 Transition Strategy


IP Version 6 - So what’s really changed ?! : IP Version 6 - So what’s really changed ?! IHL Type of Service Options Total Length Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source Address Destination Address Padding Priority Flow Label Payload Length Next Header Version Version IPv4 Header: IPv6 Header: Hop Limit Address space quadrupled to 16 bytes Fixed Length (optional headers daisy-chained) No Check sum (Done by Link Layer) No hop-by-hop segmentation (Path MTU discovery) Flow Label/Priority (Integrated QoS support) Source Address Destination Address


IPv6 Autoconfiguration : IPv6 Autoconfiguration Stateful DHCPng Addressing Lifetime Facilitates graceful renumbering Addresses defined as valid, deprecated or invalid Stateless Host autonomously configures its own address Link Local Addressing (single subnet scope, formed from reserved prefix and link layer address)


IPv6 Real Time/Premium Services support : IPv6 Real Time/Premium Services support Flow based, defines ‘flow label’ and ‘priority’ Can be combined with Source Routing header options Integration with Tag Switching/MPLS: (Reference/Draft RFC:- draft-baker-flow-label-00.txt)


IPv6 Security : IPv6 Security IPSec Architecture Export restrictions recently relaxed Authentication - MD5 based Confidentiality - DES Encrypt entire datagram or IP payload Retain existing use of (packet filtering based) firewalls


IPv6 Transition Strategy - Approaches : IPv6 Transition Strategy - Approaches Networks - Tunneling More efficient than building new IPv6 topology


IPv6 Tunneling : IPv6 Tunneling Network Address Translation IPv4 IPv6 IPv6 Driver IPv6 IPv6 IPv6 IPv4 Backbone IPv4 IPv6 Driver IPv4 Configured tunnels - manual point-2-point links Automatic tunnels - via IPv4 compatible IPv6 addresses (96 bits of zeros prefix - 0:0:0:0:0:0/96) Instrumental in building existing ‘6-Bone’ (http://www.6bone.net)


IPv6 Routing : IPv6 Routing Hierarchy is key Test address space allocation available:- (RFC 1897) Existing routing protocols extensions for IPv6 RIPv6 - Same destination/mask/metric information as RIPv2 Multiprotocol BGP4+ - Currently Draft Integrated IS-IS - 20 byte NSAP support facilitates IPv6 address/routing EIGRPv6 - Reflects Cisco’s future proofing commitment OSPFv3 - Packet formats changed to reflect 128 bits Neighbour Discovery - dynamic host router Combination of ES-IS, ARP and ICMP Redirect


IPv6 Current Status - Standardization : IPv6 Current Status - Standardization Several key components now Standards/Proposed Standards Basic Specification Neighbor Discovery RIP/OSPF ICMPv6/IGMPv6 Issues remaining open Addressing Registries Interoperability DHCP IPv6 over all media Extension Headers


IPv6 Current Status - Customers/Vendors : IPv6 Current Status - Customers/Vendors Request for IPv6 support Academic Community ISP Enterprise Vendor support:- (the usual suspects!) BAY Networks Cisco Digital Ipsilon Merit Telebit 3Com Apple FTP Software Hitachi IBM Linux NRL Siemens Nixdorf Sun … etc.


REFERENCES : REFERENCES Christian Huitema, Routing in the Internet, Prentice Hall, ISBN 013-132192-7, 1996 Kevin Dowd, “Getting Connected, Internet at 56K and Up”, O’Reilly & Associates, Inc., Bonn, 1996 Booktexts of Network Technology Workshop, National Network Management Track, Honolulu, June 1995 Craig Hunt, “TCP/IP Network Administration, O’Reilly & Associates, Inc., Sebastopol, 1993 Internetworking Technology Overview, Cisco Systems, Inc., 1993 Booktexts of the 4th Network Seminar and Intensive Course for Scientists and Network Managers from Central Europe, Feb. 1993, Vienna University Computer Center E. Comer, “Internetworking with TCP/IP”, Vol I, Principles, Protocols and Architecture, Prentice Hall, Englewood Cliffs, New Jersey, 1991. William Stallings, Data and Computer Communications, Macmillan Publishing Company, New York, 1985.